title: Analysis of a new family of widely distributed metal-independent alpha-mannosidases provides unique insight into the processing of N-linked glycans.
abstract: The modification of N-glycans by α-mannosidases is a process that is relevant to a large number of biologically important processes, including infection by microbial pathogens and colonization by microbial symbionts. At present, the described mannosidases specific for α1,6-mannose linkages are very limited in number. Through structural and functional analysis of two sequence-related enzymes, one from Streptococcus pneumoniae (SpGH125) and one from Clostridium perfringens (CpGH125), a new glycoside hydrolase family, GH125, is identified and characterized. Analysis of SpGH125 and CpGH125 reveal them to have exo-α1,6-mannosidase activity consistent with specificity for N-linked glycans having their α1,3-mannose branches removed. The x-ray crystal structures of SpGH125 and CpGH125 obtained in apo-, inhibitor-bound, and substrate-bound forms provide both mechanistic and molecular insight into how these proteins, which adopt an (α/α)(6)-fold, recognize and hydrolyze the α1,6-mannosidic bond by an inverting, metal-independent catalytic mechanism. A phylogenetic analysis of GH125 proteins reveals this to be a relatively large and widespread family found frequently in bacterial pathogens, bacterial human gut symbionts, and a variety of fungi. Based on these studies we predict this family of enzymes will primarily comprise such exo-α1,6-mannosidases.
authors.affiliation: Department of Biochemistry and Microbiology, University of Victoria, P.O. Box 3055 STN CSC, Victoria, British Columbia V8W 3P6, Canada.
authors.forename: Katie J
authors.initials: KJ
authors.lastname: Gregg
authors.forename: Wesley F
authors.initials: WF
authors.lastname: Zandberg
authors.forename: Jan-Hendrik
authors.initials: JH
authors.lastname: Hehemann
authors.forename: Garrett E
authors.initials: GE
authors.lastname: Whitworth
authors.forename: Lehua
authors.initials: L
authors.lastname: Deng
authors.forename: David J
authors.initials: DJ
authors.lastname: Vocadlo
authors.forename: Alisdair B
authors.initials: AB
authors.lastname: Boraston
mesh_terms: D002384:Catalysis; D003016:Clostridium perfringens / Q000201:enzymology*; D008670:Metals; D011134:Polysaccharides / Q000378:metabolism*; D013296:Streptococcus pneumoniae / Q000201:enzymology*; D013379:Substrate Specificity; D043323:alpha-Mannosidase / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008670:Metals; D011134:Polysaccharides; D043323:alpha-Mannosidase